Pitot static tubes are conventionally used on aircraft for measuring speed and altitude. Because of sensitivity and delicacy, such instruments are particularly prone to damage during installation, maintenance, and storage. To avoid such contamination, for any appreciable layover, the pitot static tubes are covered temporarily to prevent dust, particulates and other foreign matter from entering the probe ports. Prior to flight, the probe covers are removed.
Many aircraft, primarily commercial, also employ heating devices on the pitot static probes to prevent icing at the probe ports that can adversely affect the accuracy thereof and fire resistant materials have been developed as disclosed in U.S. Pat. No. 5,127,265 to Williamson et al. Therein, the body of the pitot static tube cover is a braided material comprised of fiberglass material that is pretreated to remove sizing and organic residue. Such design is currently in commercial usage and does provide protection against thermal degradation in the presence of inadvertent thermal cycles. Poly-aramids are also used as disclosed in my prior patent, U.S. Pat. No. 6,412,343.
While the foregoing provide effective protection, changes in pitot tube design for some aircraft pose particular difficulties in maintaining effective mounting during ground servicing constant diameter probes such as used on A300 Airbus and 757 Boeing aircraft pose a particular problem. These probes cannot use the Pitot tube tapers to assist installation and retention. Inasmuch as the interface is the fabric, the diametral control of the cover mouth has been effected by a reinforcing ring. In certain approaches, non-elastic bands have been used. The lack of flexibility limits the interference fit at the mouth cover installation that can be achieved without abrading the cover fabric. The resulting low retention force makes the cover subject to incremental movement in the presence of intermittent wind gusts and physical contact during service. Coiled springs have also been used to provide the interface biasing. Particularly in constant diameter probes without tapered entry tips, significant abrasion can occur. Moreover, there is a trend for removing any metallic content from the proximity of the engine intakes providing a need to provide a totally non-metallic cover design.